The correct option is A (i)4(ii)2(iii)1(iv)2,ABCB
Let us denote 1 with A, 2 with B, and 4 with C.
So, 1242 becomes ABCB.
The complete pattern following the rule ABCB will be:
1 2 4 2 1 2 4 2 1 2 4 2 1 2 4 2 1 2 4 2 1 2 4 2 1 2 4 2
ABCBABCBABCBABCBABCBABCBABCB
The missing links are (i)4(ii)2(iii)1(iv)2.
So, Option D is the correct answer.